As is known a scroll compressor comprises a housing with a fixed stator with a fixed scroll; and a movable rotor in this housing with a movable scroll that engages with the fixed scroll; and a crankshaft that has a main shaft that is mounted on bearings in the housing and has an eccentrically located secondary shaft with respect to the geometric axis of the main shaft that is mounted on bearings through the intervention of a ‘central bearing’ in the rotor; whereby there are means to prevent the rotation of the rotor around its centre such that the rotation of the crankshaft imposes an orbiting motion on the rotor, whereby in other words the rotor can only make a circular motion around the geometric axis of the crankshaft.
The operating principle of such type of scroll compressor is known and is based on the fact that chambers are enclosed by the motion of the rotor between the fixed scroll of the stator and the movable scroll that move from the outer periphery of the scrolls to the centre of the scrolls, whereby during this movement these chambers become increasingly smaller, such that the gas present in the chambers, such as air or another gas or mixture of gases, is compressed.
On the outer periphery of the scrolls an inlet is provided to admit fresh gas, while at the location of the centre of the scrolls an outlet is provided for the supply of compressed gas.
It is known that the compression of a gas is coupled with the generation of heat.
In the case of a scroll compressor the heat developed is partly removed via the compressed gas that leaves the scroll compressor at a relatively high temperature and partly via the rotor and stator, which are provided with cooling fins to this end and which are cooled by the freshly drawn-in gas to be compressed on the one hand, and by active air cooling whereby cold air is blown over the cooling fins of the rotor, on the other hand.
Typically the temperature of the rotor increases from the outer periphery to the centre where the aforementioned central bearing is located.
Good lubrication of this central bearing is vitally important for the lifetime and for the performance of the scroll compressor.
It is known to lubricate this central bearing with grease.
A disadvantage of grease lubrication is that only a limited speed of the rotor is allowed and consequently a limited capacity of the gas flow to be compressed.
Another disadvantage is that with grease lubrication the scroll compressor must be serviced at relatively short intervals, whereby the scroll compressor is stopped for a certain period each time.
It is also known to lubricate the central bearing using oil, which provides advantages with respect to grease lubrication in that higher rotor speeds are allowed with oil lubrication and thus a higher flow rate can be obtained and that the central bearing needs to be serviced less frequently with possibly a shorter stoppage per service.
Such a scroll compressor with oil lubrication of the central bearing is known in BE 1.009.475 and BE 1.012.016, whereby the rotor is provided with an oil chamber that is partially filled with oil and which extends from underneath the rotor to above the level of the central bearing that is connected to this oil chamber via an opening and whereby the oil is splashed upwards to against the central bearing due to the motion of the rotor.
Beyond the advantages of oil lubrication, such a known scroll compressor has another advantage in that a separate cooling circuit with a separate oil pump and pipes is not required.
However, practice shows that with such a known scroll compressor the lubrication is not always sufficient because the splashed-up oil does not circulate effectively, which can lead to damage on account of insufficient lubrication because at the location of the central bearing in the hot part of the rotor itself the oil is not sufficiently replenished and can thereby cool down insufficiently, which can lead to premature deterioration of the lubricating qualities of the oil.